Only mailables may be queued

i have to update from 5.1 to 5.4

this was code for mail with 5.1

  Mail::queue('emails.welcome_client', compact('user', 'userPassword'), function ($message) use ($user, $adminEmails) {
        $message->subject('Welcome to Enterprise Solutions!');

        $message->from(env('MAIL_FROM_ADDRESS'), env('MAIL_FROM_NAME'));
        $message->to($user->email);
        foreach($adminEmails as $adminEmail) { 
                       $message->bcc($adminEmail);
}  
});

I have to change from laravel 5.1 to 5.4 so i create object mail

here it is

<?php

 namespace App\Mail;

 use Illuminate\Bus\Queueable;
 use Illuminate\Mail\Mailable;
 use Illuminate\Queue\SerializesModels;
 use Illuminate\Contracts\Queue\ShouldQueue;

 class ClientMail extends Mailable
 {
use Queueable, SerializesModels;

/**
 * Create a new message instance.
 *
 * @return void
 */
public $user;
// protected $content;

public function __construct($user)
{

    $this->content = $user;
}

/**
 * Build the message.
 *
 * @return $this
 */
public function build()
{
    return $this->from(('MAIL_FROM_ADDRESS'), env('MAIL_FROM_NAME'))
                ->subject('Welcome to Enterprise Solutions!')
                ->view('emails.welcome_client');
    }
}

and in controller i do this

 Mail::to($user->email)
    ->bcc($adminEmail)
    ->queue(new ClientMail($adminEmails)); 
        }

when I try to run I get this error Undefined $adminEmail How I can fix this problem ?

via Chebli Mohamed